1572 "The service cannot be connected" ???

[#1]

I want to block a specific incoming call.  After searching on the Plusnet site I see I have to dial 1572 to get started.  But when I dial 1572 I get an automated message "The service cannot be connected".  What does this mean, and how can I get it "connected"?

[#2]

It sounds as if Plusnet Call Protect hasn't been enabled on your line. https://www.plus.net/home-broadband/plusnet-call-protect

[#3]

Thanks!